Ultra-high-frequency detector



Oct. 19, 1937. G. LlNDER 2,095,590

ULTRA HIGH FREQUENCY DETECTOR Filed July 27, 1937 Fig. 2.

3nventor Gttrpeg Patented Oct. 19, 1937 UNITED STATES ULTRA-HIGH-FREQUENCY DETECTOR Ernest G. Linder, Philadelphia, Pa., assignor a Radio Corporation of America, a corporation of Delaware Application July 27, 1937, Serial No. 155,984

5 Claims.

This is a refiled application corresponding in part to my abandoned application Serial No. 726,260, filed May 18, 1934, for Ultra-high-frequency detector.

This invention relates to detectors for ultrahigh frequency receiving systems and'has particular reference to the use of an electron discharge device for receiving and detecting the space energy of a transmitted beam.

In a radio receiver suitable for ultra-short waves, particularly waves of less than one meter in length, it is important that an electron discharge tube be provided wherein the cathode and the anode are brought as near together as possible in order that the time of travel of the electrons from the cathode to the anode may be made less than the periodicity of the received energy. The separation between the cathode and the anode, however, must be such as to avoid arcing when high potentials are applied therebetween.

Accordingly, it is an object of my invention to provide a detector system in which a virtual cathode may be formed in the space adjacent the anode while the filament from which the electrons are emitted is sufliciently removed from the anode to avoid arcing.

Another object of my invention is to provide a detector tube having inherently such characteristics that when suitably energized it responds directly to the presence'within its confines of space signalling energy.

Another object of my invention is to provide a system of ultra-high frequency space energy detection in which the space energy is collected by a stream of electrons in a vacuum tube, thereby effecting a. control of current flow in an output circuit for said tube.

A feature of my invention is that the electron tube utilized may be one of a numberof different types, including magnetron. diodes ancltri- .odes, also Barkhausen-Kurz split-anode tubes and tubes'for which external antenna connections may or may not be provided.

The foregoing and other objects of my invention will be best understood upon reference to the following detailed description of a number of specific embodiments when read in connection with the accompanying drawing, in which i Figure 1 is a schematic diagram of one embodiment of my invention illustrating a magnetron detectorv tube and its circuit, and

Figure 2 shows diagrammatically an embodiment in which a triode tube is employed.

According. to the generally accepted theory of operation of a magnetron tube, such as shown in Fig. 1 of the accompanying drawing, lines of magnetic force may be set up in the region between the cathode and the anode of the tube and approximately parallel to the axis of the electrodes, (assuming that the filament is straight and concentric with a cylindrical anode) and these lines of magnetic force cause the electrons to traverse arcuate paths. The magnetic force may be such, in fact, as to cause the: electrons to just barely graze the internal surface of the anode without actually striking-the anode. The relation between the magnetic force and the potential difference between the anode and the cathode can be adjusted to produce this result.

The tube then operates as a diode having a very small cathode-to-plate spacing. The minuteness ofthe spacing reduces the time of electron transit between the virtual cathode and the plate to a value lessthan an oscillation period. v

Referringto Fig. 1, I show an electron discharge tube having an envelope 1 I which has been evacuated, as usual. The tubemay comprise a filament cathode l2, and a cylindrical anode 13. In order to produce magnetic lines-of force coaxial with the electrode axis, I provide a pair of solenoids l5 which are suitably positioned with respect'to said axis. A'suitable energizing source l6 may be provided for the solenoids and, in-circuit therewith I may employ a rheostat-l1 for controlling the magnetizing force within the tube Another source of energy l8 supplies filament current to the cathode I2. Still another'source l9 supplies anode potential between the cathode and the anode. connected by an adjustable tap 33 on the potentiometer 20 with the battery IS. The output circuit includes the primary of a transformer 2|. The chokes 22 may be disposed either internally or externally of therenevelope ll,:but, for convem'ence in bringing the output circuit out through a prong of the tube base, -I pr efer to dispose thechokes internally. w The foregoing detector system does not require an antenna, as will be seen from the following discussion of the theory of operation: An electron moving in a homogeneous magnetic fielddescribes a circle whose radius'is given by :He 7 I where is the electron mass, '0 its linear velocity,

The output circuit is'preferably H the magnetic field strength, and e the electronic charge.

produce a given electronic velocity 11 is given by nzv From (1) and (2) the following equation may be derived:

2mV r f (3) Now the frequency of revolution of the electrons is Hence, if the linear velocity of the electron is increased, its frequency of revolution remains constant but its radius increases.

If the magnetic field is adjusted so that the electron frequency is equal to the frequency of the radiation passed through the tube in the direction shown by the arrow B, the electrons will move in phase with the electric field of the radiation and hence will gain velocity. As is shown by Formulas (1) and (3), this results in an increase in the radius 1. Hence, if the tube is adjusted so that in the absence of a radiation field the electrons just graze the plate, the presence of radiation in the region surrounded by the anode l3 will cause more electrons to reach the plate and hence increase the plate current. The tube will be oriented so that the radiation shall have a component of its electric vector normal to the filament, i. e., along the radius of the plate I3. The variations in plate current thus pro duced will depend upon the modulation of thereceived radiation.

Referring now to'Fig. 2, I show an embodiment of my invention having a discharge tube in which there is an accelerating grid electrode 23. In other respects the structure of the tube is similar to that of the tube shown in Fig. 1. Also, as in Fig. l, the system of Fig. 2 has inherently a selfcontained antenna system when energized. In this case, however, the velocity of the electrons may be adjusted both by the high positive potential applied to the grid electrode 23 and by the bias potential applied to the anode l3. For this purpose the potentiometer 2|] is provided with two taps, one 24 being connected in the anode circuit, and the other 25 being connected in the control grid circuit. If desired, the electrode structure of Fig. 2 may be modified, as is well understood, by providing a plurality of flat plates l3, electrically interconnected and disposed equidistant from the filament l2.

In operating this detector the grid is maintained at a high positive potential while filament and plate are at nearly zero potential. Under these conditions the electrons make radial oscillatory excursions between the filament and the plate. The frequency is given by the Barkhausen- Kurz formula where c is the velocity of wave propagation, Eg the grid potential, Ea the anode potential, Ta the anode radius and Tg the grid radius. By adjusting the plate potential Ea the electrons may be caused to approach as close as is desired to the anode as they pass through their point of maximum displacement from the grid during the cycle of oscillation.

The detecting action is similar to that of the tube shown in Fig. 1. Radiation incident upon the tube in the direction R, and such that its electric vector has a component parallel to the direction of motion of some of the electrons, accelerates these electrons, provided the electron oscillation frequency is equal to or is a sub-multiple of the radiation frequency. The amplitude of electron oscillation will increase and some electrons which would not otherwise have reached the plate will now do so. Hence the plate current will increase. The variations in plate current thus produced will depend upon the modulation of the incident radiation.

To illustrate my invention still more concretely, but without imputing any limitations to its scope, a certain magnetron tube was constructed which gave efficient results when detecting modulated energy on a carrier whose wave length was only 10 centimeters. In this case I impressed about 1000 volts on the anode, and used about 5 milliamperes for filament excitation. V The magnetic field measured 1300 gauss.

An incidental advantage to be derived from the use of detectors of the type herein disclosed may be seen from the fact that sharp resonance is possible of attainment. That is to say, the electron-containing medium behaves as a conductor of little or no resistance when adjustments are made so as to obtain resonance between the output circuit and the received wave. Hence the invention may be advantageously used to detect frequency shifts.

It is, of course, to be understood that detectors of the type described herein may be used with reflectors, particularly those of parabolic shape such as will concentrate the received radio ener gy within the zone of electronic action. When de tectors of the type shown in Figs. 1 and 2 are used, the filament should be placed at the focus of the parabolic reflector.

Although I have disclosed herein certain specific means for accomplishing the objects of my invention, these are given merely by way of example and are not to be construed as limiting the scope of my invention. Other modifications will suggest themselves to those skilled in the art. My invention, therefore, is not to be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I'claim as my invention:

1. The method of receiving and demodulating space energy of an ultra-high frequency beam which comprises producing an electron discharge in an evacuated zone having a cathodical axis and an anodical periphery, orienting said axis coaxially with the direction from which said beam is received, producing a constant field of magnetic force in said zone with the lines'thereof approximately parallel to said cathodical axis, thereby causing the electrons of said discharge to describe arcuate paths, causing said space energy to control the radius of curvature of said paths, and producing a space current in said zone the amplitude of which varies with variations in said radius.

2. An ultra-high frequency detector system comprising an electron discharge device having an anode, a cathode and an accelerating electrode; means for applying potentials to said electrodes so that an electron discharge is caused to oscillate in and out of said accelerating electrode, and means for adjusting said potentials so that the oscillatory action of said electrons may be controlled by the presence within the midst thereof of radiated space signalling energy, whereby said energy is demodulated.

3. The method of receiving and demodulating space energy of an ultra-high frequency beam which comprises producing an electron discharge in an evacuated zone having a cathodical axis and an anodical periphery, adjusting the speed of the electrons constituting said discharge in accordance with the frequency of the beam to be demodulated, producing a constant field of magnetic force in said zone with the lines thereof approximately parallel to said cathodical axis thereby causing the electrons of said discharge to describe arcuate paths, orienting said axis coaxially with the direction of said beam, causing said space energy to control the radius of curvature of said paths, and producing a space current in said zone the amplitude of which varies with variations in said radius.

4. A magnetron translating device having an anode and a cathode, means for exciting said cathode to render it electron-emitting, an output circuit including a source of potential and a load connected between said electrodes, means for setting up a substantially constant magnetic flux in the region between said cathode and anode, the density of said magnetic flux and the value of said potential being so chosen with respect to the frequency of the waves to be translated that the device responds directly to control by space propagated waves present in said region.

5. An ultra-high frequency detector system comprising an electron discharge device including anode and cathode electrodes, means for applying potentials to said electrodes to thereby establish an electron discharge from said cathode,

means for causing said electrons to oscillate between said anode and cathode, and means for adjusting said potentials so that the oscillatory action of said electrons may be controlled by the presence within the midst thereof of radiated space signalling energy, whereby said energy is demodulated.

ERNEST G. LINDER. 

